import numpy as np

from .base_cam import BaseCAM


class GradCAM(BaseCAM):
    def __init__(self, model, target_layers, reshape_transform=None):
        super(GradCAM, self).__init__(model, target_layers, reshape_transform)

    def get_cam_weights(
        self, input_tensor, target_layer, target_category, activations, grads
    ):
        # 2D image
        if len(grads.shape) == 4:
            return np.mean(grads, axis=(2, 3))

        # 3D image
        elif len(grads.shape) == 5:
            return np.mean(grads, axis=(2, 3, 4))

        else:
            raise ValueError(
                "Invalid grads shape."
                "Shape of grads should be 4 (2D image) or 5 (3D image)."
            )
